If you have a can of beans and some milk... you're in luck.
But -- Just for the record, my healthy substitute does NOT taste like Alfredo. It has a good flavor, one I appreciate, but it is not Alfredo. I highly recommend it atop veggies and pasta (a great way to clean out the fridge too!).
Healthy White Sauce - SnoWhite
1 can Great White Northern beans, drained
3 T - 1/4 C milk (as needed)
1/4 C Parmesan cheese
Spices (like basil), if desired
Begin by draining and rinsing your beans.
Then, place beans in the blender along with a few T of milk. Puree, adding more milk as needed to create a creamy sauce to your desired thickness.
I usually end up using about 1/4 C milk to make my sauce.
Pour sauce over your pasta or veggies while they are still heating in the pan. Add the cheese and any spices you want to add to your sauce.
Stir to melt cheese and warm sauce.
It's a nice change from a traditional white sauce. Frog Prince (who doesn't like beans) enjoys the sauce too, although his comment is often that it's not as creamy as he'd like. The sauce does dry out pretty easily, so adding more milk when re-heating the dish is helpful. You'll have to take creative liberties with the milk to achieve the desired consistency of the sauce.